A phage-displayed single chain variable fragment that interacts with hepatitis B core antigen: Library construction, selection and diagnosis

Background - Phage display is an alternative method for constructing and selecting antibodies with desired specificity towards an antigen. Objectives - To construct a library of single chain variable fragment (ScFv) towards hepatitis B core antigen (HBcAg). To isolate a ScFv phage clone that interacts with HBcAg and to develop a phage-ELISA for detecting the antigen. Study design - Mice were inoculated with HBcAg and RNA was extracted from their spleen cells. The genes encoding heavy (VH) and light (VL) chains were amplified, linked via PCR and cloned into a phagemid vector. Phage particles displaying ScFv were panned against HBcAg and a selected clone was characterized and employed as a diagnostic reagent for detecting HBcAg in serum samples. Results - A phage clone that interacts with HBcAg was selected from the antibody library. The binding of the phage to HBcAg was inhibited by a cyclic peptide bearing the WSFFSNI sequence. A phage-ELISA was established using the recombinant phage and as low as 10 ng of HBcAg can be detected by the assay. Conclusion - The ScFv displayed on the surface of filamentous phage is an alternative choice for diagnosis of HBcAg in serum samples